1. Field of the Invention
The present invention generally relates to a method of generating exposure data, and particularly relates to a method of generating exposure data for use in designing a reticle mask.
Increases in circuit density of semiconductor integrated circuit have been brought about by rapid technological development, and integrated-circuit manufacturing devices are expected to demonstrate enhanced performance to satisfy the demand for a further increase in circuit density. In the art of fine process technology, more sophisticated techniques are required to keep up with increases in pattern density of integrated circuits.
The present invention is directed to a method of processing data which defines each pattern of a reticle when the reticle is designed by use of a CAD device. Here, the reticle is a mask used in an exposure process for manufacturing an integrated circuit.
Density of reticle patterns needs to be increased in order to increase circuit density, which results in an increase in an exposure-data size as the exposure data is used for patterning a reticle. When an efficiency of a process of generating a reticle is taken into consideration, a data processing method needs to be optimized. To this end, the exposure-data size needs to be reduced. Also, steps of generating exposure data and a method of processing data need to be simplified.
2. Description of the Related Art
It is a widely employed practice to use a CAD (computer aided design) device when designing a reticle mask (hereinafter referred to simply as a reticle). FIGS. 1 through 3F are illustrative drawing showing a procedure for designing a reticle by using a CAD device.
A related-art procedure for designing a reticle by using a CAD device will be described below.
As shown in FIG. 1, a host computer 10 of a CAD system sends design data 16 to a data processing unit 12. The data processing unit 12 converts the design data 16 into exposure data 18, and sends the exposure data 18 to the exposure unit 14. At a time of exposure, light emitted form a light source 21 is controlled by a polarization plate 22 in terms of an exposure position thereof on a reticle 23.
A pattern formed in a reticle is comprised of figures which serve as a unit element constituting the pattern. A figure or a set of figures is called a cell. A plurality of cells together constitute a pattern in the reticle.
When an exposure device is to form various patterns on a semiconductor device, figures constituting each of these patterns are drawn on the reticle. As a result, the reticle ends up having areas with figures and blank areas without figures. In order to generate figures, data representing the figures is allocated by the CAD device to positions where figures are supposed to be present. The data obtained after such positional allocation is called exposure data, and constitutes cells. The blank areas without figures do not have data allocated thereto, and are called non-exposure areas.
A procedure for generating exposure data in the related art will be described with reference to accompanying drawings.
In order to generate exposure data, design data needs to be generated first that serves as a basis of the exposure data.
FIG. 2 is a flowchart of a process of generating design data. FIGS. 3A through 3F are illustrative drawings showing the way the data is generated in each cell at each step of the process of FIG. 2.
In FIGS. 3A through 3F, a blackened area in each cell indicates where design data exists, and areas without a black mark do not have design data allocated thereto. In FIGS. 3A through 3F, a TOP cell is a cell at the highest level in a hierarchy, and cells a through d belong to the next highest level. All the cells together form a library. It should be noted that the TOP cell does not have any design data therein, and that the cells a through d is provided with respective design data.
At a step S1 in FIG. 2, a cell A and the cells a through d are generated, where the cells a through d have respective design data generated therein. Namely, as shown in FIG. 3A, the cell A is provided with design data 36, and the cells a through d are provided with design data 26, 28, 30, and 32, respectively.
At a step S2 in FIG. 2, the cells A (24) are arranged in a 2-by-2 matrix at a lower level under a TOP cell 34 by arranging the design data 36. This is shown in FIG. 3B.
At a step S3 in FIG. 2, as shown in FIG. 3C, the design data 26 of the cell a is generated in one of the cells A (24) arranged at the lower level under the TOP cell 34.
At a step S4 in FIG. 2, as shown in FIG. 3D, the design data 28 of the cell b is generated in one of the cells A (24) arranged at the lower level under the TOP cell 34.
At a step S5 in FIG. 2, as shown in FIG. 3E, the design data 30 of the cell c is generated in one of the cells A (24) arranged at the lower level under the TOP cell 34.
At a step S6 in FIG. 2, as shown in FIG. 3F, the design data 32 of the cell d is generated in one of the cells A (24) arranged at the lower level under the TOP cell 34.
FIG. 4A is a flowchart of a process of generating exposure data based on the design data which is created as described above. The exposure data is to be used when patterning of a reticle is carried out.
As shown in FIG. 4A, the design data generated by the steps S1 through S6 of FIG. 2 as shown in FIGS. 3A through 3F is inverted by a design-data inverting device (will be described later) to generate exposure data.
FIG. 4B is an illustrative drawing for explaining the inversion of design data.
When a pattern is actually formed on a reticle, the pattern needs to permit a passage of light in the areas where the design data 36, 26, 28, 30, and 32 are present as shown in FIG. 4B. For this purpose, the design data should be inverted. Namely, the exposure data is created in an area 38 where the design data is not present, and is not created in the areas 36, 26, 28, 30, and 32 where the design data is present.
FIG. 5 is a flow diagram showing the way the design data is converted into the exposure data through inversion of the design data. Each step of FIG. 4A corresponds to each step of FIG. 5.
A reticle pattern is created based on the exposure data generated as described above, and is then used to expose posi-resist on a semiconductor substrate to exposure light at the black portion of FIG. 5 where the exposure data exists (i.e., the area 38 shown at the step S3). This exposure process results in a photoresist pattern being formed. During generation of the design data as described above, the design data is processed as data having a hierarchical structure. The exposure data, on the other hand, is not processed as data having a hierarchical structure. This results in an increase in a data size of the exposure data.
In general, when data items of a given data group need to be stored as files, each data item is stored as a separate file if each data item is different. In this case, there is no hierarchical structure. When some of the data items share common data, sharing of the common data can be reflected in a file structure by introducing a hierarchy. The larger the number of data items, the more efficient the introduction of a hierarchy can be.
In the related-art method of generating exposure data as previously described, the exposure data of each cell has a different configuration, and this prevents hierarchical data processing. When every single cell has to possess exposure data including a common data portion, the exposure-data size increases in proportion to an increase in the number of matrix. This leads to a massive data size of the exposure data. Also, the number of data processing steps for generating the exposure data will increase. Because of all of this, the related-art method of generating the exposure data is not preferable when an efficiency is taken into consideration.
In what follows, a description will be given with regard to problems encountered when the hierarchical processing is introduced to the related-art method of generating exposure data.
FIG. 6 is a flowchart showing a method of generating the design data, and FIGS. 7A through 7F are illustrative drawings showing the way the design data is arranged at each step of FIG. 6. In this related-art method, the cells a through d are arranged on the matrix provided within the TOP cell in the same manner as in the method described in connection with FIG. 2 and FIGS. 3A through 3F.
Instead of generating exposure data from the design data generated in this manner, hierarchical data processing can be applied as in the following manner whatever the efficacy of such an application may be.
FIG. 8A is a flowchart of a process of generating exposure data based on design data while each cell is treated separately, and FIG. 8B is an illustrative drawing for explaining the cell-wise inversion of design data to generate the exposure data.
FIG. 9 is a flow diagram showing the way the design data of each cell is converted into the exposure data while each cell is treated separately.
As shown in FIG. 9, the cell A and the cells a through d, which would be arranged in a 2-by-2 matrix in the above-mentioned method of generating the design data, are treated separately, and the design data of each of these cells is inverted to generate exposure data MAIN1 through MAIN5.
After this, the exposure data MAIN1 is arranged in a 2-by-2 matrix at a lower level under the TOP cell, and the exposure data MAIN2 through MAIN5 are superimposed on the exposure data MAIN1 in the same manner as in the method of generating design data. Since superimposition of the exposure data results in double exposure, however, an appropriate exposure process cannot be carried out in such a configuration. In reality, therefore, hierarchical data processing cannot be implemented.
Accordingly, there is a need for a scheme for hierarchical data processing which is workable, can reduce an exposure-data size, and can simplify the data processing steps of generating exposure data.
Accordingly, it is a general object of the present invention to provide a scheme for hierarchical data processing which can satisfy the needs described above.
It is another and more specific object of the present invention to provide a scheme for hierarchical data processing which is workable, can reduce an exposure-data size, and can simplify the data processing steps of generating exposure data.
In order to achieve the above objects according to the present invention, a method of generating exposure data includes the steps of generating first exposure data representing a common portion shared by different exposure images, generating second exposure data representing portions which differ between the different exposure images, and defining at least one non-exposure area with regard to the first exposure data, the at least one non-exposure area corresponding to the portions that differ between the different exposure images and defining an area where no exposure is performed by the first exposure data.
In the method as described above, exposure data is created to reflect a hierarchical structure thereof. Namely, the first exposure data represents the common-data portion shared by the different exposure images, which may be arranged in a matrix form, for example. The portions that differ between these exposure images are represented by the second exposure data. Such separation of data reflecting its hierarchical structure is made possible by use of the non-exposure area. Since the common-data portion is extracted and can be stored as a file, there is no need to store the entire exposure data as a single data file as in the related-art scheme by retaining its matrix form, for example. Therefore, the present invention reduces the data size of the exposure data by a significant amount compared to the related-art scheme.
According to another aspect of the present invention, a method of printing a pattern on a reticle by using exposure data includes the steps of generating first exposure data representing a common portion shared by different exposure images, generating second exposure data representing portions which differ between the different exposure images, defining at least one non-exposure area with regard to said first exposure data, said at least one non-exposure area corresponding to the portions that differ between the different exposure images and defining an area where no exposure is performed by said first exposure data, printing an image of the common portion on the reticle as many times as there are the different exposure images by using said first exposure data with no exposure being performed at said at least one non-exposure area, and printing images of said second exposure data at the portions which differ between the different exposure images.
In the method described above, the first exposure data is used for printing the image of the common portion with respect to each of the exposure images while the non-exposure area is left unprinted, and the second exposure data is used for printing the images of the different portions at the non-exposure area in each of the exposure images. In this manner, an appropriate printing process is performed without getting a trouble of double exposure while the exposure data is provided in a hierarchical structure.